The present invention relates to friction clutches, especially for motor vehicles, and is more particularly directed to the unitary assembly which is incorporated in such a clutch, as described for example in the documents FR-A-2 242 892 and FR-A-2 420 690. Such a unitary assembly is called a clutch mechanism.
A clutch mechanism conventionally comprises a reaction plate which is part of an engine flywheel, which may be divided into two parts so as to constitute, in particular, a torsion damped flywheel.
The reaction plate is fixed in rotation to a first shaft, such as a driving shaft, namely the crankshaft of the internal combustion engine in the context of application to a motor vehicle.
This reaction plate has a dorsal friction face, and is fixed in rotation to a pressure plate which is able to be displaced axially with respect to the reaction plate, also referred to as the engine flywheel.
The pressure plate has a front friction face.
The friction liners of a friction disc are interposed between the pressure plate and the reaction plate, and more precisely between the friction faces of these latter.
These liners are fixed to a support which is usually axially deformable elastically. In another version, the support is rigid, being for example encapsulated at its outer periphery within a single friction liner. The said support, which may be double, is rigidly or elastically connected to a hub which is fixed in rotation to a second shaft, such as a driven shaft, namely the input shaft of a motion transmission means, for example a gearbox in the context of application to a motor vehicle.
When the friction liners are gripped between the pressure plate and reaction plate (clutch engaged), the torque is transmitted from the driving shaft to the driven shaft via the friction disc. When the friction liners are not gripped between the said plates (clutch disengaged), the driven shaft is not driven by the driving shaft. For this purpose, axially acting clutch engaging means are provided, and constitute a unit with declutching means which are arranged to counteract, when required, the action of the clutch engaging means bearing on a cover plate, so as to act on the pressure plate, and more precisely so as to act on engagement means carried by the pressure plate, which is fixed in rotation to the cover plate while being able to be displaced axially with respect to the latter, for example with the aid of a coupling using axially elastic tongues, or with the aid of a tenon and mortice type coupling, in which radial lugs, forming tenons, of the pressure plate are engaged for axial sliding movement in grooves, forming mortices, of the cover plate.
The cover plate has at its outer periphery fastening means for securing it to the reaction plate, either detachably or permanently.
The clutch engaging means include at least one Belleville ring, and the declutching means include declutching levers for acting on the clutch engaging means. Usually, these clutch engaging and declutching means are part of one common component, elastic in the axial direction, which is a so-called diaphragm. This diaphragm, which is of frusto-conical form in the free state, has a peripheral portion in the form of a Belleville ring, which is extended radially towards the centre by a central portion divided into radial fingers by blind slots with widened bases, to define widened apertures at the inner periphery of the Belleville ring that constitutes the axially acting clutch engagement means, while the radial fingers constitute declutching levers and therefore the declutching means of the clutch.
In the documents FR-A-2 242 892 and FR-A-2 420 690, the cover plate constitutes, with the pressure plate, the resilient tongues and the diaphragm, a unitary assembly or so-called clutch mechanism which is fixed on the reaction plate. This clutch mechanism may of course constitute, with the friction disc and the reaction plate, a module which is attached in a unitary manner on the crankshaft of the engine of the vehicle or on a radial plate fixed to the crankshaft, with the reaction plate then being secured on the radial plate, which is preferably flexible.
This mechanism may be equipped with a wear compensating device for the friction liners and the friction faces of the pressure plate and reaction plate, in order that the diaphragm can be in a substantially constant position when the clutch is engaged, over the working life of the friction clutch.
This wear compensating device usually comprises ramps and counter-ramps which act between the pressure plate and the engagement means of the diaphragm, or between the diaphragm and the cover plate. An initiator, which is sensitive to the state of wear in the friction liners, enables the ramps to be rotated in the event of wear in order that the diaphragm will always occupy the same position when the clutch is engaged under the action of the clutch engaging means (liners gripped).
The initiator may include an elastic wear sensor or a system having a ratchet wheel and a worm, incorporated in a cassette.
Other versions may be envisaged.
In the documents mentioned above, the cover plate has a base portion, oriented transversely and open in the centre, and including abutment lugs at its inner periphery.
It is on these transversely oriented abutment lugs that the fingers of the diaphragm bear when the clutch mechanism is no longer fixed on the reaction plate. This position is called the storage position. In this position the diaphragm is inclined by a large amount, and the pressure plate projects axially with respect to the free end of the cover plate.
The pressure plate is further away in the axial direction from the base portion of the cover plate than it is when the clutch is in its engaged condition. In that condition the diaphragm is generally flat.
As can be seen in the document FR-A-2 242 892, the abutment lugs are spaced apart circumferentially at regular intervals with the fastening lugs of the diaphragm, so as to mount the diaphragm for tilting movement between a primary abutment and a secondary abutment, these abutments being carried by the cover plate.
The abutment lugs are separated therefore in pairs by slots, in the middle of which the fastening lugs are located.
The primary abutment is formed by press-forming the cover plate, and the secondary abutment is defined by the fastening lugs extending through the widened apertures in the diaphragm. As can be seen in FIG. 2 of the document FR-A-2 420 690, the secondary abutment is of course carried, in another version, by a crown ring.
The abutment lugs may also be fastening lugs and may in particular carry rivets or small fastening posts, or any other means, as described in the document FR-A-2 420 690.
An object of the present invention is to make use of the abutment lugs in a simple and inexpensive way.
According to the invention, a mechanism of the type defined above is characterised in that a support member carries at its outer periphery locating lugs which project radially outwards, in that the support member is in contact with at least a plurality of the declutching levers, while the locating lugs are in contact with the face of the abutment lugs facing towards the declutching levers, so that the locating lugs and the support member are inserted axially between the declutching levers and the abutment lugs by a connection of the bayonet type.
Thanks to the invention, the locating lugs and the support member together constitute a locating means or spacer which is inserted axially, in one embodiment, between the diaphragm and the abutment lugs, so as to maintain the diaphragm in a predetermined position during assembly and/or disassembly of the clutch mechanism.
The support member, with its locating lugs, constitutes an assembly and/or dismantling tool for the clutch mechanism. It also acts as a tool for protection of, especially, the resilient tongues which couple the pressure plate in rotation with the cover plate.
In all cases, it is possible to avoid modifying the cover plate. The declutching levers can of course be part of a false diaphragm that includes an external peripheral portion in the form of an annular ring of low axial elasticity, or even without any axial elasticity, which is extended by a central portion divided into radial fingers by slots. The fingers constitute the declutching levers in the same way as the fingers of the diaphragm. The ring may be provided with blind radial slots which are open at the outer periphery of the ring, so that the latter will not be axially elastic, or will have only little axial elasticity. The false diaphragm is adapted to act on a Belleville ring constituting the clutch engaging means.
Thus in all cases declutching levers are provided which are mounted for pivoting or tilting movement by virtue of fastening means carried by the cover plate, and the support member with its locating lugs constitutes locating means which enables the clutch mechanism to be delivered in a position that corresponds to the clutch engaged position, that is to say in a position in which the pressure plate is retracted into the interior of the cover plate.
The clutch mechanism is then shorter in the axial direction, which facilitates its fitting on the reaction plate, the friction liners being, before it is mounted and fitted, interposed between the pressure plate and reaction plate.
In addition, the screws for fastening the cover plate to the reaction plate can be shorter and therefore less costly, because the pressure plate is retracted inside the cover plate. The female threads formed in the reaction plate for screwing in the fastening screws are also shorter, so that the strength of the reaction plate is increased.
These fastening screws may be replaced by rivets or other fastening members, shorter axially because of the invention.
The solution provided by the invention is therefore inexpensive and facilitates fastening of the cover plate, because the diaphragm is delivered in a position which corresponds to the clutch engaged position when the mechanism is fixed on the reaction plate.
Thus, the force which is exerted by the diaphragm is smaller than the maximum load which the latter can exert. During screwing or riveting of the cover plate in position on the reaction plate, and having regard to the interposition of the friction liners between the pressure and reaction plates, there is no need to displace the pressure plate from an initial position to a position corresponding to the maximum value of the force exerted by the diaphragm on the pressure plate, because the diaphragm is already beyond that position.
During this assembly operation, the friction disc is inserted between the pressure and reaction plates so that, having regard to the above mentioned position of the diaphragm, it only remains to compress the elastic support of the friction liners.
The fastening screws are then easily tightened. The same is true when the cover plate is fixed on the reaction plate, for example by seaming. The same is again true when the clutch engaging means consist of a Belleville ring.
This configuration is relevant in the case where the clutch mechanism is equipped with a wear compensating device, because the assembly leads to a configuration in which the clutch is in the engaged position appropriate for a new clutch (with unworn friction liners).
Because of the locating lugs according to the invention, the diaphragm can be slightly inclined, that is to say it can be put in a position for starting a declutching operation.
In that case there is no need during assembly to compress the support of the friction liners.
Fastening of the cover plate is even easier; the pressure plate can be stripped during assembly with respect to the friction liners.
It can therefore be seen that lugs according to the invention can be used for dismantling a module. In this connection it is possible to dismantle the reaction plate directly without having to dismantle the clutch mechanism.
Therefore, since the pressure plate has been stripped with respect to the friction liners, it is enough to put the holes formed in the friction disc and in the diaphragm into axial alignment with each other. The unscrewing tool is then passed through the said aligned holes so as to give access to the heads of the screws fastening the reaction plate to the crankshaft, and to unscrew the screws and dismantle the module. In another version, the mechanism is mounted on a double damped flywheel having radial springs and a small bearing fitted radially inward of the passage holes formed in the reaction plate, as described in the document FR-A-2 716 511.
The diaphragm may of course be inclined in the other direction.
In all cases, the wear compensating device, and especially the resilient member carried by the cassette of the latter or its elastic wear detecting member, is protected. In this connection, because of the support member having the locating lugs, the pressure plate can easily be finally fixed without damaging the wear compensating device.
The lugs according to the invention are therefore assembly and/or disassembly and/or protective lugs.
The circumferential width of the lugs according to the invention may be either smaller or greater than that of the abutment lugs.
The outer diameter of the locating lugs is preferably less than that of the internal diameter of the fastening lugs or fastening posts, or any other means for fastening the diaphragm carried by the abutment lugs.
In general terms, the locating lugs according to the invention are introduced into the slots that separate the abutment lugs in pairs, and then, by acting on the support member of the locating lugs, the diaphragm is deformed in the region of its inner end by an amount greater than the required position of the diaphragm, and finally the support member is rotated so as to bring the lugs of the invention under the abutment lugs.
After this rotation the force exerted on the support member is released, the latter being preferably in the form of a circular plate open in the centre, or in another version in the form of an open circular arch. The circumferential width of the locating lugs therefore depends on the circumferential width of the slot that exists between consecutive abutment lugs, in order that the abutment lugs can penetrate into the slots for the bayonet connection.
In order to rotate the abutment lugs, the support member is provided with apertures. These apertures, such as holes, also enable the tool or tools for screwing and unscrewing the screws fastening the reaction plate to the crankshaft of the engine to be inserted.
It can thus be seen that the cover plate is able to be fixed permanently to the reaction plate, for example by welding or seaming, so as to constitute a module with the friction disc.
The support member may of course be in the form of an annular ring with lugs at its inner periphery for rotating it.